Absolute humidiometer

ABSTRACT

An instrument for measuring absolute humidity by comparing the attenuation of Lyman-alpha radiation through a reference chamber containing a dry gas with the attenuation through a sample chamber containing moist gas. The optical path lengths of the two chambers are matched by varying the length of the sample chamber. The outputs of the respective nitric oxide detectors, which measure the intensity of radiation transmitted through the chambers, are compared directly by a differential amplifier circuit to provide an output indicative of the absolute humidity of the sample.



1. An instrument for measuring absolute humidity comprising: a radiation source for emitting Lyman-alpha radiation in at least two directions; first and second hollow chambers, each having a pair of aligned apertures formed therein and each being positioned to receive Lyman-alpha radiation from said source through one of said apertures, said first and second chambers each having one aperture hermetically sealed to a portion of said radiation source to receive radiation into said chambers; first and second radiation detectors, each received in the other respective aperture of said chambers for producing electrical signals proportional to The amount of radiation impinging upon said detectors, said first detector being hermetically mounted within said first chamber, said second detector being hermetically and adjustably mounted within said second chamber for selectively varying the distance between said second detector and said radiation source; and circuit means for comparing said signals and providing an output proportional to the difference between said signals, whereby, when a dry gas is introduced into said first chamber and a sample of like gas containing water vapor is introduced into said second chamber, the output of said circuit means is indicative of the absolute humidity of the sample gas.
 2. The device of claim 1 wherein: said first chamber includes fluid inlet and outlet ports formed therein for passing a dry reference gas through the first chamber, and said second chamber includes fluid inlet and outlet ports formed therein for passing a sample gas containing water vapor through the second chamber.
 3. The device of claim 2 wherein said circuit means includes: first and second preamplifiers coupled to said first and second detectors respectively, a differential amplifier coupled to said preamplifiers for providing an output proportional to difference of the outputs of said first and second detectors, and a zero-center meter for indicating the output of said differential amplifier as a function of absolute humidity.
 4. The device of claim 1 wherein said first and second detectors each comprise an ionization chamber containing nitric oxide gas and having a lithium fluoride window forming one wall thereof to receive the radiation from said source into the ionization chambers. 